
    <!DOCTYPE html>
    <html lang="zh-CN">
    <head>
      <meta charset="UTF-8">
      <meta name="viewport" content="width=device-width, initial-scale=1.0">
      <title>1、 String - 交互式测验</title>
      <style>
        @import url('https://fonts.googleapis.com/css2?family=Noto+Sans+SC:wght@400;500;700&display=swap');
        
        body {
          font-family: 'Noto Sans SC', sans-serif;
          background-color: #f4f7f9;
          color: #333;
          display: flex;
          justify-content: center;
          align-items: center;
          min-height: 100vh;
          margin: 0;
          padding: 20px;
          box-sizing: border-box;
        }
        
        .main-wrapper {
            position: relative;
            width: 100%;
            max-width: 900px; /* Wider to accommodate buttons */
            display: flex;
            justify-content: center;
            align-items: center;
        }

        .quiz-container {
          background-color: #ffffff;
          border-radius: 16px;
          box-shadow: 0 8px 32px rgba(0, 0, 0, 0.1);
          width: 100%;
          max-width: 700px;
          overflow: hidden;
          z-index: 10;
        }

        .quiz-header {
          background-color: #4a90e2;
          color: white;
          padding: 20px 30px;
          text-align: center;
        }

        .quiz-header h1 {
          margin: 0;
          font-size: 24px;
          font-weight: 700;
        }
        
        .quiz-header p {
            margin: 5px 0 0;
            font-size: 14px;
            opacity: 0.9;
        }

        .quiz-body {
          padding: 30px;
        }

        .progress-bar {
            display: none; /* 隐藏进度条 */
            width: 100%;
            background-color: #e0e0e0;
            border-radius: 5px;
            height: 10px;
            margin-bottom: 20px;
        }

        #progress-indicator {
            height: 100%;
            width: 0%;
            background-color: #4caf50;
            border-radius: 5px;
            transition: width 0.3s ease;
        }

        #question-container {
          margin-bottom: 20px;
        }

        #question-text {
          font-size: 18px;
          font-weight: 500;
          line-height: 1.6;
          margin-bottom: 25px;
        }

        .options-list {
          list-style: none;
          padding: 0;
          margin: 0;
        }

        .option-item {
          background-color: #f8f9fa;
          border: 1px solid #dee2e6;
          border-radius: 8px;
          padding: 15px;
          margin-bottom: 12px;
          cursor: pointer;
          transition: background-color 0.2s ease, border-color 0.2s ease;
        }

        .option-item:hover {
          background-color: #e9ecef;
        }
        
        .option-item.selected {
            background-color: #d1e7fd;
            border-color: #4a90e2;
        }

        .quiz-footer {
          padding: 20px 30px;
          display: flex;
          justify-content: space-between; /* 将按钮分布在两侧 */
          align-items: center;
          min-height: 65px; /* Reserve space */
        }

        .nav-btn {
          background-color: #4a90e2;
          color: white;
          border: none;
          border-radius: 8px;
          padding: 10px 20px;
          font-size: 16px;
          font-weight: 500;
          cursor: pointer;
          transition: background-color 0.2s ease, transform 0.2s ease;
          box-shadow: 0 4px 12px rgba(0,0,0,0.15);
        }
        
        #next-btn {
            background-color: #28a745;
        }

        .nav-btn:hover {
          background-color: #357abd;
          transform: scale(1.05);
        }
        
        .nav-btn:disabled {
            background-color: #a0c3e8;
            cursor: not-allowed;
            opacity: 0.7;
        }

        #result-container {
            border-top: 1px solid #eee;
        }
        
        .result-box {
            border-radius: 8px;
            padding: 20px;
            margin-top: 20px;
        }
        
        .result-box.correct {
            background-color: #d4edda;
            border: 1px solid #c3e6cb;
            color: #155724;
        }

        .result-box.incorrect {
            background-color: #f8d7da;
            border: 1px solid #f5c6cb;
            color: #721c24;
        }
        
        .result-box h3 {
            margin-top: 0;
        }

        .explanation-text {
            margin-top: 15px;
            line-height: 1.7;
        }
        
        .source-text {
            font-style: italic;
            font-size: 14px;
            margin-top: 15px;
            color: #555;
        }

        
        .final-score-container {
            padding: 40px;
            text-align: center;
        }
        .final-score-container h2 {
            margin-top: 0;
            margin-bottom: 30px;
        }
        .score-summary {
            display: flex;
            justify-content: center;
            gap: 20px;
            margin-bottom: 40px;
            flex-wrap: wrap;
        }
        .score-card {
            background-color: #f8f9fa;
            border-radius: 12px;
            padding: 20px;
            width: 180px;
            box-shadow: 0 4px 12px rgba(0,0,0,0.05);
            border: 1px solid #e9ecef;
        }
        .score-card h3 {
            margin: 0 0 10px;
            font-size: 16px;
            font-weight: 500;
            color: #555;
        }
        .score-card p {
            margin: 0;
            font-size: 28px;
            font-weight: 700;
            color: #333;
        }
        .score-details table {
            width: 100%;
            font-size: 16px;
        }
        .score-details td {
            padding: 4px 0;
        }
        .score-details td:last-child {
            text-align: right;
            font-weight: 700;
        }
        .report-actions button {
            background-color: #fff;
            border: 1px solid #ccc;
            border-radius: 8px;
            padding: 12px 25px;
            font-size: 16px;
            cursor: pointer;
            margin: 0 10px;
            transition: background-color 0.2s ease, border-color 0.2s ease, transform 0.2s ease;
        }
        .report-actions button:hover {
            background-color: #f1f1f1;
            border-color: #bbb;
            transform: translateY(-2px);
        }
        .report-actions button.primary {
            background-color: #28a745;
            color: white;
            border-color: #28a745;
        }
        .report-actions button.primary:hover {
            background-color: #218838;
        }
        
        .hint-container {
            background-color: #e0f7fa;
            border: 1px solid #b2ebf2;
            border-radius: 8px;
            padding: 15px;
            margin-top: 20px;
            color: #006064;
            font-size: 15px;
            line-height: 1.6;
            display: none; /* 默认隐藏 */
        }
      </style>
    </head>
    <body>
      <div class="main-wrapper">
          <div class="quiz-container">
            <div class="quiz-header">
              <h1>1、 String - 交互式测验</h1>
              <p>检验你对文档内容的理解程度</p>
            </div>
            <div id="quiz-content">
                <div class="quiz-body">
                    <div class="progress-bar">
                        <div id="progress-indicator"></div>
                    </div>
                    <div id="question-container">
                      <p id="question-text"></p>
                      <ul class="options-list" id="options-list"></ul>
                    </div>
                    <div id="result-container"></div>
                    <div id="hint-container" class="hint-container"></div>
                </div>
                <div class="quiz-footer" id="quiz-footer">
                  <button id="prev-btn" class="nav-btn">上一题</button>
                  <button id="hint-btn" class="nav-btn" style="background-color: #ffc107; color: #333; box-shadow: 0 4px 12px rgba(255,193,7,0.3);">提示</button>
                  <button id="next-btn" class="nav-btn">下一题</button>
                </div>
            </div>
          </div>
      </div>

      <script>
        const quizData = [
  {
    "question": "根据文档，以下哪项不是Java中String类被设计为不可变（immutable）所带来的好处？",
    "options": [
      "由于对象状态无法改变，它天然是线程安全的。",
      "可以缓存其哈希码（hashCode），提高在哈希表结构中的性能。",
      "在进行频繁的字符串拼接操作时，性能最高。",
      "不可变性是实现字符串常量池（String Pool）优化的基础。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "String的不可变性意味着每次修改（如拼接）都会创建一个新的String对象，这在频繁操作时会导致性能下降和大量内存开销。因此，文档明确指出，在这种场景下应使用StringBuilder或StringBuffer。其他选项（线程安全、哈希码缓存、支持常量池）都是不可变性带来的直接好处。",
    "source": "文档中「2.2 String 的不可变性及其好处」和「2.3 性能优化：StringBuilder vs StringBuffer」部分",
    "hint": "思考一下，当你在一个循环中用 `+` 连接字符串时，为什么会被建议使用其他类？"
  },
  {
    "question": "在Java 9之后，String的内部实现从`char[]`改为了`byte[]`，这样做的主要目的是什么？",
    "options": [
      "为了提升字符串查找（indexOf）操作的速度。",
      "为了更好地兼容不同的操作系统文件编码。",
      "为了在大多数字符串只包含Latin-1字符时节省一半的内存空间。",
      "为了让String类能够支持更大的字符串长度。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "文档中明确指出，从Java 9开始，String内部实现改为`byte[]`并增加一个`coder`字段，是为了进行内存优化。因为在实际应用中，绝大部分字符串是ASCII或Latin-1字符，每个字符只需1个字节即可存储，而`char`类型固定占用2个字节。这种改变可以在存储这类字符串时节省约一半的内存。",
    "source": "文档中「2.1 从 char[] 到 byte[]」部分",
    "hint": "文档中提到，`char`需要2个字节，而很多常见字符实际上只需要1个字节。"
  },
  {
    "question": "执行以下代码后，`s1 == s3`的结果是什么？\n`String s1 = \"Java\";`\n`String s2 = new String(\"Java\");`\n`String s3 = s2.intern();`",
    "options": [
      "false，因为s2是在堆上创建的新对象。",
      "true，因为`intern()`方法会返回字符串常量池中对应字符串的引用。",
      "不确定，取决于JVM的实现。",
      "编译错误，不能对new出来的对象调用intern()。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "s1是通过字面量创建的，它的引用指向字符串常量池。s2是通过`new`关键字创建的，它是在堆内存中的一个新对象。`s2.intern()`方法会检查常量池中是否存在内容为“Java”的字符串，如果存在（在此场景下，s1已经使其存在），则返回常量池中的那个引用。因此，s3和s1将指向同一个对象。",
    "source": "文档中「1.3 字符串常量池」部分",
    "hint": "回顾一下 `intern()` 方法的作用：它会尝试将字符串放入常量池并返回池中的引用。"
  },
  {
    "question": "在单线程环境中，如果需要在一个循环内拼接大量字符串，以下哪个类是性能最佳的选择？",
    "options": [
      "String，因为编译器会自动优化。",
      "StringBuffer，因为它能保证线程安全。",
      "StringBuilder，因为它非线程安全，避免了同步开销。",
      "String.format()，因为它提供了灵活的格式化功能。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "文档的对比表格和性能测试代码清晰地表明：在单线程环境下，`StringBuilder`性能最高，因为它不会像`StringBuffer`那样进行同步操作，从而减少了不必要的开销。虽然编译器会对简单的`+`拼接进行优化，但在循环中，这种优化是有限的，每次循环仍可能创建新的`StringBuilder`对象，而手动在循环外创建`StringBuilder`是最佳实践。",
    "source": "文档中「2.3 性能优化：StringBuilder vs StringBuffer」和「2.4 字符串拼接的编译器优化」部分",
    "hint": "在单线程场景下，线程安全机制是一种不必要的性能开销。"
  },
  {
    "question": "考虑以下代码：`String str = \"Hello World\"; String result = str.replace(\"l\", \"L\");`。执行后，原始字符串`str`的值是什么？",
    "options": [
      "HeLLo WorLd",
      "Hello World",
      "null",
      "这段代码会抛出异常，因为String是final的。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "这是对String不可变性的核心考察。String的所有修改方法（如`replace`, `substring`, `toLowerCase`等）都不会改变原始字符串对象本身，而是会返回一个包含了修改后结果的*新*的String对象。因此，原始字符串`str`的值在`replace`方法调用后仍然是“Hello World”。",
    "source": "文档中「1.1 String 的本质」和「2.2 String 的不可变性及其好处」部分",
    "hint": "String最重要的特性之一是“不可变性”（immutability）。"
  },
  {
    "question": "在处理用户输入时，为了避免`NullPointerException`，以下哪种字符串比较方式是文档中推荐的安全做法？",
    "options": [
      "if (userInput.equals(\"admin\")) { ... }",
      "if (userInput == \"admin\") { ... }",
      "if (\"admin\".equals(userInput)) { ... }",
      "if (userInput.intern() == \"admin\") { ... }"
    ],
    "correctAnswerIndex": 2,
    "explanation": "文档在“避免空指针异常”一节中明确指出，将字符串字面量（常量）放在`equals()`方法的调用方是一种安全的实践。因为即使变量`userInput`为`null`，调用`\"admin\".equals(null)`也只会返回`false`，而不会抛出`NullPointerException`。相反，`userInput.equals(\"admin\")`在`userInput`为`null`时会触发空指针异常。",
    "source": "文档中「3.2.1 避免空指针异常」和「4.1 字符串比较：== vs equals()」部分",
    "hint": "如果一个变量可能是 `null`，你就不应该尝试调用它的任何方法。"
  },
  {
    "question": "当需要替换字符串中的*所有*点号 `.` 为下划线 `_` 时，为什么使用`replace('.', '_')`通常比`replaceAll(\"\\.\", \"_\")`更高效？",
    "options": [
      "`replace`方法是异步执行的，而`replaceAll`是同步的。",
      "`replaceAll`方法基于正则表达式，引擎的初始化和匹配过程有性能开销，而`replace`进行的是简单的字符序列查找替换。",
      "`replace`可以一次性替换所有匹配项，而`replaceAll`需要多次查找。",
      "这两种方法在性能上没有显著差异，只是用法不同。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "文档在“正则表达式陷阱”部分通过性能对比指出，`replaceAll`方法使用正则表达式作为其第一个参数。即使是简单的匹配，也需要编译和执行正则表达式，这带来了额外的性能开销。而`replace`方法执行的是字面量（CharSequence）的查找和替换，不涉及正则引擎，因此在不需要正则表达式的场景下，它的性能要高得多。",
    "source": "文档中「4.2 正则表达式陷阱」部分",
    "hint": "`replaceAll` 的 'All' 并不意味着比 `replace` 替换得更多，它们的功能区别在于第一个参数的类型。"
  }
];
        console.log("Quiz Data:", JSON.parse(JSON.stringify(quizData))); // 添加这行用于调试，以可展开的JSON格式输出
        
        let currentQuestionIndex = 0;
        let score = 0;
        // 存储每个问题的回答状态
        const userAnswers = new Array(quizData.length).fill(null); 

        const questionTextEl = document.getElementById('question-text');
        const optionsListEl = document.getElementById('options-list');
        const resultContainerEl = document.getElementById('result-container');
        const quizContentEl = document.getElementById('quiz-content');
        const progressIndicatorEl = document.getElementById('progress-indicator');
        const prevBtn = document.getElementById('prev-btn');
        const nextBtn = document.getElementById('next-btn');
        const hintBtn = document.getElementById('hint-btn');
        const hintContainerEl = document.getElementById('hint-container');

        function loadQuestion() {
          resultContainerEl.innerHTML = '';
          optionsListEl.innerHTML = '';
          hintContainerEl.style.display = 'none'; // 隐藏提示
          
          if (currentQuestionIndex >= quizData.length) {
            showFinalScore();
            return;
          }

          updateProgress();

          const currentQuestion = quizData[currentQuestionIndex];
          questionTextEl.textContent = `(${currentQuestionIndex + 1}/${quizData.length}) ${currentQuestion.question}`;
          
          currentQuestion.options.forEach((optionText, index) => {
            const li = document.createElement('li');
            li.className = 'option-item';
            li.textContent = optionText;
            li.dataset.index = index; // Store index in a data attribute
            // 如果这道题已经回答过，恢复状态
            if (userAnswers[currentQuestionIndex] !== null) {
                if (index === userAnswers[currentQuestionIndex]) {
                    li.classList.add('selected');
                }
            }
            optionsListEl.appendChild(li);
          });

          // 如果已经回答过，直接显示结果
          if (userAnswers[currentQuestionIndex] !== null) {
              const isCorrect = userAnswers[currentQuestionIndex] === currentQuestion.correctAnswerIndex;
              showResult(isCorrect, currentQuestion);
          }
          
          updateNavigationButtons();
          updateProgress();
        }

        function selectOption(optionIndex) {
            userAnswers[currentQuestionIndex] = optionIndex;
            const currentQuestion = quizData[currentQuestionIndex];
            const isCorrect = optionIndex === currentQuestion.correctAnswerIndex;

            // 重新计算分数
            score = userAnswers.reduce((acc, answer, index) => {
                return answer === quizData[index].correctAnswerIndex ? acc + 1 : acc;
            }, 0);

            showResult(isCorrect, currentQuestion);
            updateNavigationButtons();
        }
        
        function updateProgress() {
            const answeredQuestions = userAnswers.filter(answer => answer !== null).length;
            const progressPercentage = (answeredQuestions / quizData.length) * 100;
            progressIndicatorEl.style.width = `${progressPercentage}%`;
        }
        
        function updateNavigationButtons() {
            prevBtn.style.display = 'block';
            nextBtn.style.display = 'block';
            hintBtn.style.display = 'block'; // 显示提示按钮

            prevBtn.disabled = currentQuestionIndex === 0;
            nextBtn.disabled = false; // 最后一题时，下一题按钮不禁用，而是用于显示报告
            nextBtn.textContent = (currentQuestionIndex === quizData.length - 1) ? '查看报告' : '下一题';
            
            // 如果当前问题没有提示，则禁用提示按钮并隐藏提示内容
            if (!quizData[currentQuestionIndex].hint) {
                hintBtn.disabled = true;
                hintContainerEl.style.display = 'none';
                hintContainerEl.textContent = ''; // 清除旧的提示内容
            } else {
                hintBtn.disabled = false;
            }
        }

        function showResult(isCorrect, questionData) {
            resultContainerEl.innerHTML = ''; // 清空之前的结果
            const resultBox = document.createElement('div');
            resultBox.className = `result-box ${isCorrect ? 'correct' : 'incorrect'}`;
            
            let html = `<h3>${isCorrect ? '回答正确！' : '回答错误'}</h3>`;
            if (!isCorrect) {
                html += `<p><strong>正确答案是：</strong> ${questionData.options[questionData.correctAnswerIndex]}</p>`;
            }
            html += `<div class="explanation-text">${questionData.explanation}</div>`;
            html += `<div class="source-text">来源: ${questionData.source}</div>`;
            
            resultBox.innerHTML = html;
            resultContainerEl.appendChild(resultBox);

            // 禁用所有选项的点击事件，并高亮正确/错误答案
            Array.from(optionsListEl.children).forEach((child, index) => {
                child.style.pointerEvents = 'none';
                // 高亮正确答案
                if (index === questionData.correctAnswerIndex) {
                    child.classList.add('correct'); // 需要添加CSS样式
                    child.style.backgroundColor = '#d4edda';
                    child.style.borderColor = '#c3e6cb';
                }
                // 如果选错了，高亮错误选项
                if (!isCorrect && index === userAnswers[currentQuestionIndex]) {
                    child.classList.add('incorrect'); // 需要添加CSS样式
                    child.style.backgroundColor = '#f8d7da';
                    child.style.borderColor = '#f5c6cb';
                }
            });
        }

        function goToNextQuestion() {
            if (currentQuestionIndex < quizData.length - 1) {
                currentQuestionIndex++;
                loadQuestion();
            } else {
                showFinalScore();
            }
        }

        function goToPreviousQuestion() {
            if (currentQuestionIndex > 0) {
                currentQuestionIndex--;
                loadQuestion();
            }
        }
        
        function showHint() {
            const currentQuestion = quizData[currentQuestionIndex];
            if (currentQuestion.hint) {
                hintContainerEl.textContent = currentQuestion.hint;
                hintContainerEl.style.display = 'block';
            } else {
                hintContainerEl.style.display = 'none';
            }
        }

        function showFinalScore() {
            document.querySelector('.quiz-body').style.display = 'none';
            document.getElementById('quiz-footer').style.display = 'none';

            const correctCount = score;
            const totalQuestions = quizData.length;
            const answeredCount = userAnswers.filter(a => a !== null).length;
            const wrongCount = answeredCount - correctCount;
            const skippedCount = totalQuestions - answeredCount;
            const accuracy = totalQuestions > 0 ? Math.round((correctCount / totalQuestions) * 100) : 0;
            const errorRate = totalQuestions > 0 ? Math.round((wrongCount / totalQuestions) * 100) : 0;

            const finalScoreHtml =
                '<div class="final-score-container">' +
                '<h2>答题报告</h2>' +
                '<div class="score-summary">' +
                '<div class="score-card">' +
                '<h3>得分</h3>' +
                '<p>' + correctCount + ' / ' + totalQuestions + '</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>正确率</h3>' +
                '<p>' + accuracy + '%</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>错误率</h3>' +
                '<p>' + errorRate + '%</p>' +
                '</div>' +
                '<div class="score-card score-details">' +
                '<table>' +
                '<tr><td>正确</td><td>' + correctCount + '</td></tr>' +
                '<tr><td>错误</td><td>' + wrongCount + '</td></tr>' +
                '<tr><td>未答</td><td>' + skippedCount + '</td></tr>' +
                '</table>' +
                '</div>' +
                '</div>' +
                '<div class="report-actions">' +
                '<button id="review-btn">回顾测验</button>' +
                '<button class="primary" onclick="location.reload()">再试一次</button>' +
                '</div>' +
                '</div>';

            let reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }
            quizContentEl.insertAdjacentHTML('beforeend', finalScoreHtml);
            document.getElementById('review-btn').addEventListener('click', reviewQuiz);
        }

        function reviewQuiz() {
            const reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }

            document.querySelector('.quiz-body').style.display = 'block';
            document.getElementById('quiz-footer').style.display = 'flex';
            
            currentQuestionIndex = 0;
            loadQuestion();
            updateNavigationButtons(); // Ensure nav buttons are correctly displayed
        }

        // Event Delegation for options
        optionsListEl.addEventListener('click', (event) => {
            if (event.target && event.target.matches('li.option-item')) {
                // Check if the question has already been answered
                if (userAnswers[currentQuestionIndex] === null) {
                    const selectedIndex = parseInt(event.target.dataset.index, 10);
                    selectOption(selectedIndex);
                }
            }
        });

        prevBtn.addEventListener('click', goToPreviousQuestion);
        nextBtn.addEventListener('click', goToNextQuestion);
        hintBtn.addEventListener('click', showHint);
        
        // 初始加载
        loadQuestion();
      </script>
    </body>
    </html>
  